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United States Patent |
5,755,100
|
Lamos
|
May 26, 1998
|
Hermetically sealed stirling engine generator
Abstract
A hermetically sealed Stirling engine driven generator system with a
rotating generator, self lubricated bearings using PTFE filled polyimide,
a fibrous ceramic piston dome, and flame sprayed ceramic and PTFE coating
on the pistons, which allow an oil free system. A brushless self starting
system is also used as an alternator. A simple working gas pressure
control system uses the housing for the generator and the crankcase as a
reservoir for working gas allowing a single valve working in conjunction
with a small compressor to regulate the pressure of the working gas.
Inventors:
|
Lamos; Richard A. (Christiansted, VI)
|
Assignee:
|
Stirling Marine Power Limited (St. Croix, VI)
|
Appl. No.:
|
823349 |
Filed:
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March 24, 1997 |
Current U.S. Class: |
60/521; 60/524 |
Intern'l Class: |
F01B 029/10 |
Field of Search: |
60/521,524,526
|
References Cited
U.S. Patent Documents
3492324 | Jan., 1970 | Johansson et al. | 60/524.
|
3813881 | Jun., 1974 | Neelen | 60/521.
|
3999388 | Dec., 1976 | Nystrom | 60/521.
|
4179891 | Dec., 1979 | Gronvall | 60/521.
|
4253303 | Mar., 1981 | Liljequist | 60/517.
|
4511805 | Apr., 1985 | Boy-Marcotte | 290/1.
|
4765138 | Aug., 1988 | Corey | 60/517.
|
5329768 | Jul., 1994 | Moscrip | 60/518.
|
Primary Examiner: Kamen; Noah P.
Claims
What I claim is:
1. A Stirling cycle engine driven generator, said generator being
operatively connected to an external load or source, said Stirling cycle
driven generator comprising:
a sealed housing, said housing being filed with a gaseous fluid, said
gaseous fluid being pressurized to a pressure above atmospheric pressure;
a compression piston having a first side and a second side opposite said
first side movably mounted within said housing, said compression piston
being in sealed engagement with said housing and restricting the passage
of said gaseous fluid between said first side of said compression piston
and said second side of said compression piston;
an expansion piston having a first side and a second side opposite said
first side movably mounted within said housing, said expansion piston
being in sealed engagement with said housing and restricting the passage
of said gaseous fluid between said first side of said expansion piston and
said second side of said expansion piston; a mechanical connection means
which connects said second side of said expansion piston and said second
side of said compression piston in such a way as to cause oscillatory
movement of said expansion piston and said compression piston, the
relative movement of said pistons defining a phase angle, said phase angle
being essentially 90 degrees;
said mechanical connection means further containing a rotatably mounted
member which rotates in concert with the said oscillatory movement of said
pistons; a compression space within said housing having one side defined
by said first side of said compression piston, said compression space
containing a working fluid; an expansion space within said housing having
one side defined by said first side of said expansion piston, said
expansion space containing said working fluid, said working fluid being
the same material as said gaseous fluid;
said expansion space and said compression space being in communicating
relationship so as to allow said working fluid to flow between said
expansion space and said compression space in response to said oscillatory
movement of said expansion piston and said compression piston;
a cooler in a heat transferring relationship with said working fluid in
said compression space;
a heater in a heat transferring relationship with said working fluid in
said expansion space;
a generator armature rotatably mounted within said housing, said armature
connected to said rotatably mounted member of said mechanical connection
means;
a generator stator mounted within said housing in such a way as to act in
conjunction with said armature so as to produce electrical current when
said armature rotates.
2. A Stirling cycle engine driven generator according to claim 1 further
comprising a regenerator in a heat transferring relationship with said
working fluid such that heat is stored in said regenerator while said
working fluid travels from said expansion space to said compression space
and heat is regained by said working fluid from said regenerator as said
working fluid travels from said compression space to said expansion space
whereby efficiency is improved.
3. A Stirling cycle engine driven generator according to claim 1 wherein
said mechanical connection means is a crankshaft.
4. A Stirling cycle engine driven generator according to claim 3 wherein
said mechanical connection comprising self lubricated journal bearings.
5. A Stirling cycle engine driven generator according to claim 4 wherein
said self lubricated journal bearings contain PTFE filled polyimide.
6. A Stirling cycle engine driven generator according to claim 1 wherein
said compression piston and said expansion piston are coated with a flame
sprayed coating containing ceramic and PTFE.
7. A Stirling cycle engine driven generator according to claim 6 wherein a
fibrous ceramic dome is affixed to said first side of said expansion
piston.
8. A Stirling cycle engine driven generator according to claim 7 wherein
said pumping means includes a compressor piston connected to said
compression piston.
9. A Stirling cycle engine driven generator according to claim 8 wherein
said compressor piston includes a valve.
10. A Stirling cycle engine driven generator according to claim 1 further
comprising a pumping means for moving said gaseous fluid contained within
said housing from said second side of said compression piston to the said
first side of said compression piston whereby pressure is increased in
said working fluid.
11. A Stirling cycle engine driven generator according to claim 10 further
comprising a valving means for controlling the flow of said working fluid
from the said compression space to said housing whereby the pressure of
said working fluid is regulated.
12. A Stirling cycle engine driven generator according to claim 11 wherein
said valving means contains a proportional control valve and a
microprocessor controller.
13. A Stirling cycle engine driven generator according to claim 1 further
comprising a pumping means for moving said gaseous fluid contained within
said housing from said second side of said expansion piston to the said
first side of said expansion piston whereby pressure is increased in said
working fluid.
14. A Stirling cycle engine driven generator according to claim 1 further
comprising a self starting means.
15. A Stirling cycle engine driven generator according to claim 14 wherein
said self starting means is used to generate an electrical current while
said Stirling cycle engine is in operation.
16. A Stirling cycle engine driven generator according to claim 14 wherein
said self starting means comprises a starter stator and a starter rotor,
with said starter stator affixed to said housing and said starter rotor
rotatably connected to said mechanical connection means.
17. A Stirling cycle engine driven generator according to claim 16 wherein
said starter stator and said generator stator are one and the same and
said starter rotor and said generator armature are one and the same.
18. A Stirling cycle engine driven generator according to claim 16 further
comprising an electronic commutation means for supplying electrical
current to said stator.
19. A Stirling cycle engine driven generator according to claim 18 wherein
said commutation means includes a sensing means selected from the group
consisting of optical sensors, Hall effect sensors, capacitive sensors,
proximity sensors and magnetic sensors.
20. A Stirling cycle engine driven generator according to claim 1 wherein
the said heater comprises a plurality of passages for containing and
transporting said working gas;
a domed shaped cylinder head connected to said passages;
a cylindrical shell for directing combustion gasses past said passages and
said cylinder head;
an annular recuperator having inlet air channels and exhaust gas channels
with inlets and exits of said channels at both ends;
an exhaust duct which communicates with said exhaust gas channels of said
recuperator;
an inlet air duct which communicates with said inlet air channels of said
recuperator such that incoming air is heated by said exhaust gasses;
a vaporization tube which communicates with said inlet air duct;
an electronic fuel injector which communicates with said vaporization tube,
and an igniter positioned a predetermined distance from said vaporization
tube, whereby said fuel injector injects fuel through the said
vaporization tube where it is heated and mixed with air before exiting
said vaporization tube where it is ignited and burned by said igniter.
Description
BACKGROUND--FIELD OF INVENTION
The present invention relates to a Stirling engine, and more particularly
to a hermetically sealed unit suitable for use in producing electricity.
BACKGROUND--DISCUSSION OF PRIOR ART
The Stirling engine is an external combustion engine that converts heat
into driving power by continuous heating and cooling of a captive gas. The
engine operates on the principle that a gas (in this case helium) expands
when heated and contracts when cooled. Many different embodiments have
been disclosed in the past including swashplate drives, rhombic drives,
free piston engines, and more. The simplest design remains the standard
crankshaft driving two pistons contained within cylinders positioned
ninety degrees from each other. A variety of heat sources can be used, the
most common is an external combustion chamber in which a combustible fuel
is burned in an abundance of air at atmospheric pressure. There is no
debris or unburned fuel to be disposed of, and there are no byproducts of
combustion coming into contact with the moving parts of the engine. Heater
tubes within the combustion chamber are connected to the cylinders and to
a water cooled heat exchanger. This closed system contains helium, the
working gas, which moves back and forth between the combustion chamber and
the heat exchanger where heat is rejected to the cooling system water.
This action of heating and cooling the helium changes its pressure and
exerts a force on the pistons that drive the crankshaft. To control the
speed, the Stirling engine has two control systems. The first control
keeps the temperature of the working gas at a constant value by varying
the air flow and the fuel flow. The second control system maintains a
constant speed by opening and closing valves that regulate the pressure of
the working gas.
Previously, all embodiments of the Stirling engine have had problems that
have prevented them from being viable products. All systems that utilize
an output shaft as their way of extracting work from the engine have a
difficult problem in sealing the high pressure working gas (helium or
hydrogen) within the system. Previous embodiments have tried techniques
such as using a cross head with a cylindrical piston shaft which is
sealed. This seal requires lubricating oil to be pumped against the seal
to retard the leakage of the gas and to lubricate the seal. This presents
the problem of oil contamination of the working gas. U.S. Pat. No.
4,765,138 to Corey (1988) discloses a pressurized crankcase to eliminate
the cross heads and connecting rods. This system, however, just moves the
problem to the crankshaft where seals are required. It also requires that
the crankshaft be cooled to prevent the deterioration of the connecting
rod bearings.
U.S. Pat. No. 4,511,805 to Boy-Marcotte et al. (1985) discloses a "free
piston" Stirling engine in which the pistons are coupled to a linear
alternator and the system is hermetically sealed. The free piston system
is difficult to counterbalance and requires complex electromagnetic
coupling and control systems as is witnessed by U.S. Pat. No. 5,329,768 to
Moscrip (1994). It is also limited by the mass of the linear alternator
which must be constantly accelerated and decelerated back and forth, and
there are no commercially available alternators of this type. Another
embodiment is shown in U.S. Pat. No. 4,253,303 to Liljequist (1981) which
uses a bellows arrangement to seal in the working gas. This system is
impractical in that the working pressure of the gas must be kept low to
minimize stress on the bellows which greatly reduces the efficiency of the
engine. The output of the engine is also linear which is impractical to
use for productive work.
Previous embodiments of the Stirling engine have required complex control
systems to maintain their speed over a range of load conditions. Systems
which have dynamic seals need to have a reservoir of helium or hydrogen to
make up for losses during running and to reduce pressure so that leakage
is minimized when the engine is not running. These reservoirs require
valves and piping to allow the gas to be moved to and from the engine,
adding to the cost and complexity of the system.
OBJECTS AND ADVANTAGES
It is, therefore, an object of the present invention to provide an improved
Stirling engine powered generator system with a simplified design
including a hermetically sealed housing containing all that is necessary
for self starting and the production of electricity, and provides a
reservoir for the working gas which eliminates the problems of sealing in
the working gas. Another advantage of the present invention is the
elimination of lubricating oil by the use of a combination of new
materials.
It is another object of the present invention to provide a system for speed
control, thus regulating the frequency of the electrical output, which is
simplified and less costly to produce. It is a further object of this
invention to provide a highly reliable, quiet, low vibration system with
all the other advantages of the Stirling engine technology.
Additional benefits and advantages of the present invention will become
apparent to those skilled in the art to which this invention relates from
the following description of the preferred embodiments and the claims,
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an overall perspective view of an embodiment of a Stirling engine
driven generator system in accordance with the present invention.
FIG. 2 is a sectional view of the major components of an embodiment of the
Stirling engine of the present invention.
FIG. 3 is an enlarged partial sectional view of the compressor of FIG. 2.
FIG. 4 is an exploded isometric view of the Stirling engine of FIG. 2 less
the burner components.
FIG. 5 is an exploded isometric view of the burner components and the
assembled Stirling engine of FIG. 2.
FIG. 6 is an isometric view of the Stirling engine of FIG. 2 with an
exploded view of the starter components and bell housing of the generator
system of FIG. 1.
FIG. 7 is an exploded isometric view of the generator components and
housing of the Stirling engine generator system of FIG. 1.
REFERENCE NUMERALS IN THE DRAWINGS
______________________________________
10 crankcase
12 expansion piston
14 compression piston
16 crankshaft
18 connecting rod
20 cooler
22 regenerator
24 igniter
26 vaporization tube
28 air deflector
30 recuperator
32 heater assembly
34 compression cylinder
36 expansion cylinder
38 compressor piston
40 ball valve
42 compressor rod
44 compressor spring
46 compressor wrist pin
48 compressor head
50 compressor valve
52 pressure control valve
54 pressure control tube
56 compressor tube
58 air inlet duct
60 exhaust duct
62 wrist pin
64 liner
66 cylinder gasket
68 cooler end caps
70 piston rings
72 connecting rod bearings
74 dome
76 head gasket
78 main bearing
80 bearing plate
82 speed sensor
84 speed sensor disk
86 fuel injector
88 bell housing
90 starter stator
92 starter rotor
94 flywheel
96 generator armature
98 generator stator
100 generator cooling tubes
102 generator housing
104 temperature sensor
106 ceiling
______________________________________
DETAILED DESCRIPTION OF THE INVENTION
The preferred embodiment of this invention is shown in perspective view in
FIG. 1. It consists of a crankcase 10 which supports an expansion cylinder
36 and a compression cylinder 34. The axis of these cylinders are
substantially 90 degrees from each other. FIG. 1 also shows a bell housing
88 attached and sealed to the crankcase 10. Attached and sealed to the
bell housing 88 is a generator housing 102.
FIG. 2 is a sectional view cut through the crankcase 10, the expansion
cylinder 36, and the compression cylinder 34. The expansion cylinder is
jacketed such that cooling water can be circulated around it. The
compression cylinder 34 is made up of two regions which are cylindrical
and co-linear. One of these regions is significantly smaller in diameter
than the other. This assembly is also water jacketed to accommodate
cooling water. Fastened to the top of the compression cylinder 34 is a
compressor head 48. A cooler 20 is also attached to compression cylinder
20 in such a way as to allow the passage of a pressurized working gaseous
fluid between them. The cooler 20 is fitted with internal cooling passages
and with end caps 68 though which water can pass, forming a heat exchanger
to transfer heat form the working gas to the water. Connected to the
cooler is a regenerator 22 which is filled with metallic filaments and
provides a passageway from the cooler to a heater assembly 32. This heater
assembly is made up of a multiplicity of tubes and an annular passageway
which are integrally welded to a domed shaped section. This heater
assembly 32 is also connected to the expansion cylinder 36.
A compressor tube 56 is connected between the crankcase 10 and the
compressor head 48 in such a way as to form a gas-tight passageway between
them. A pressure control tube is connected between the crankcase 10 and
the upper end of the larger diameter region of the compression cylinder
34. The pressure control tube 54 contains a pressure control valve 52.
Within the crankcase 10 is a crankshaft 16 onto which are connected two
connecting rods 18 which share a common journal. Two wrist pins 62 connect
rods 18 to a compression piston 14 and a expansion piston 12. A multiple
of piston rings 70 are fitted within grooves in the compression piston 14
and the expansion piston 12, forming a sufficiently tight seal as to
greatly restrict the passage of high pressure gas between the inner walls
of the cylinders and the pistons. Rigidly attached to expansion piston 12
is a fibrous ceramic dome 74.
Surrounding the heater assembly 32, is a burner assembly consisting of a
cylindrical liner 64, a recuperator 30, an air inlet duct 58, and an
exhaust duct 60. A vaporization tube 26 consists of a curved hollow tube
which passes through and is welded to a flat sheet metal ceiling 106 which
forms the right end of a combustion chamber. The ceiling 106 is fitted
with a hole through its center through which air can pass. Attached to
ceiling 106 at this point is an air deflector 28 which is made up of
angularly arranged vanes which cause a swirling of the air that passes
through the opening in the ceiling 106. An igniter 24 is screwed into a
hole in the center of the air deflector 28 in such a manner as to provide
a spark gap between the electrode of the igniter 24 and the vaporization
tube 26. A solenoid type electronic fuel injector 86 is attached to inlet
air duct 58 and projects through a hole within it such that the discharge
end is inline with the vaporization tube 26.
Attached to the compression piston 14 is a compressor piston 38, via a
compressor rod 42. FIG. 3 shows an enlarged sectional view of the
compressor piston 38 and its associated parts which are contained in a
cylindrical passageway which is contained within the compression cylinder
34. Compressor piston 38 is connected to compressor rod 42 by a compressor
wrist pin 46. A ball valve 40 is held against a tapered seating surface
within compressor piston 38 by a compressor spring 44. There is a small
hole through the end of the compressor piston 38 such that a one-way valve
is formed which allows working gas to pass downward through the piston and
into the space below it, but not upward through the compressor piston 38.
A compressor valve 50 is sandwiched between the compressor head 48 and the
compression cylinder 34. This compressor valve 50 is a thin reed type
valve which is positioned in a way such that it allows the passage of the
working gas downward through the compressor head 48 into the space above
compressor piston 38, but not upwardly through the compressor head 48.
FIG. 4 is an exploded isometric view of the Stirling engine of FIG. 2
without the burner parts. Also seen in FIG. 4 are two cylinder gaskets 66
which form a gas-tight seal between the crankcase 10 and the compression
cylinder 34, and between the expansion cylinder 36 and the crankcase 10. A
head gasket 76 forms a gas-tight seal between the expansion cylinder 36
and the heater assembly 32. This head gasket 76 is made of a synthetic
asbestos-like material which acts as a thermal insulator. The crankshaft
16 is supported by two main bearings 78, one of which is supported by a
bearing plate 80, and the other is fitted within crankcase 10. An optical
speed sensor 82 is mounted on the bearing plate 80. A speed sensor disk is
attached to the crankshaft 16 such that it works in conjunction with the
speed sensor 82.
FIG. 5 shows the Stirling engine of FIG. 4 along with an exploded isometric
view of the burner parts. The exhaust duct 60 is provided in two halves so
that it can be fitted around the heater assembly 32 and forms a manifold
for collecting the exhaust gasses. Recuperator 30 is made up of a hollow
cylindrical inner shell, a hollow cylindrical outer shell and a corrugated
sheet metal piece which fills the gap between the two shells.
FIG. 6 shows the Stirling engine assembly of FIG. 5 along with an exploded
isometric view of the bell housing 88 and a starter assembly made up of a
starter stator 90, which is fastened to the bell housing 88, and a starter
rotor 92 which is fastened to a flywheel 94. The flywheel 94 is fastened
to the crankshaft 16.
FIG. 7 shows the Stirling engine assembly of FIG. 6 along with an exploded
isometric view of the generator assembly. The generator assembly is made
up of a generator armature 96 which is fastened to flywheel 94, and a
generator stator 98, which is fastened to bell housing 88. A set of
cooling tubes 100 surround the generator stator 98. These cooling tubes
100 are arranged such that they can pass through and be hermetically
sealed to a generator housing 102, which is attached and sealed to bell
housing 88.
Operation of the Invention
Referring to FIG. 2, air for combustion is introduced through air inlet
duct 58 by a blower or other means and is forced to flow through passages
within the recuperator 30 which are formed between the outer surface of
the corrugated piece and the inner surface of the outer cylindrical shell.
This combustion air picks up heat from the recuperator. The combustion air
is then forced to enter the volume formed between the ceiling 106 and the
inner surface of the air inlet duct 58, as can be seen by the arrows of
FIG. 2. A small amount of the combustion air is forced to enter two small
holes in the side of the vaporization tube 26. A metered amount of fuel is
sprayed into the vaporization tube by the fuel injector 86. The hot
vaporization tube vaporizes the fuel as it is mixed with the air entering
the tube. As this fuel-air mixture exits the vaporization tube, it is met
by the bulk of the combustion air which passes through the opening in the
ceiling 106 and is set into a swirling motion by the air deflector 28. At
the point of departure of the air fuel mixture from the vaporization tube,
a high voltage spark is formed between the igniter 24 and the end of the
vaporization tube. Combustion occurs at this point and the combustion
gasses are directed to flow past the tubes and domed section of the heater
assembly 32, by the liner 64. These combustion gasses are then forced to
flow through the passages of the recuperator 30 formed between the inner
surfaces of the corrugated piece and the inner cylindrical shell, thus
heating the incoming combustion air and cooling the out-going combustion
gasses. A constant temperature of the working gas within the heater
assembly can be maintained by regulating the fuel flow and the air flow by
the use of pulse width modulation of the fuel injector and voltage control
of the blower motor by a micro-computer or other suitable means. Complete
combustion of the fuel can be achieved with "blue flame" combustion from
many liquid combustible fuels, such as a diesel, gasoline, alcohol,
gasohol, or kerosene. Because there is an abundance of incoming air at
atmospheric pressure, the level of unburned hydrocarbons is low as well as
producing low carbon monoxide levels.
In order to set the crankshaft 16 into motion, the starter system of FIG. 6
is employed. It consists of a permanent magnet rotor which is fastened to
the flywheel 94. The starter stator 90 which is rigidly fastened to the
bell housing 88, receives electrical pulses from a battery or other means,
through an electronic circuit according to the input from the optical
speed sensor 82. Light beams are intermittently interrupted within the
sensor by the speed sensor disk, in such a way as to provide commutation
of the electrical field in the stator causing the rotor to rotate and thus
the crankshaft 16 also to rotate. When the crankshaft rotates in a
counterclockwise fashion as seen in FIG. 2, the compression piston 14
moves upward and the expansion piston 12 moves to the left The working gas
that is contained within the system is forced to move from above the
compression piston through the cooler 20 and the regenerator 22, and into
the heater assembly 32. The working gas picks up heat from the hot
surfaces of the heater assembly and expands, forcing the expansion piston
down. The dome 74 which is constructed of a fibrous ceramic material
provides thermal insulation from the working gas and keeps the expansion
piston from over heating.
As the crankshaft continues to rotate in a counter clockwise fashion, the
two pistons continue their 90 degree phase relation movement within the
cylinders. As the expansion piston begins to move from left to right, the
working gas is forced through the heater assembly into the regenerator
where some of its heat is stored in metallic filaments contained within
it. The gas then passes through the cooler around its cooling tubes. Water
is pumped through these tubes and also around the compression cylinder 34,
within its water jacket The working gas gives up a significant amount of
its heat in these areas. As the crankshaft continues to rotate, the
compression piston moves upwardly compressing the working gas, and also
moving it back through the system to the heater assembly. As it passes
through the regenerator it regains some of the heat that it stored there
on its way through previously. As this process continues, moving the gas
back and forth between the compression side where it is compressed and the
expansion side where it expands, speed of rotation increases due to the
work done on the pistons by the working gas. Once a predetermined speed is
reached, the electrical pulses to the starter are discontinued. After this
happens, the starter becomes an alternator whose output can be rectified
and used to charge the battery used to start the engine.
In order to regulate the angular velocity of the crankshaft and therefore
the velocity of the generator armature which is fastened to it, it is
necessary to regulate the pressure of the working gas within the working
space. This space is defined by the volume within the cylinders as bounded
by the pistons and the volume contained within the heater assembly, the
regenerator, and the cooler. As the compression piston moves up and down
within the larger diameter portion of the compression cylinder, it carries
with it the compressor piston 38 which moves up and down within the
smaller diameter section of the compression cylinder. During the "up
stroke" the reed type compressor valve 50, is forced closed by the
increasing pressure of the working gas trapped above the compressor
piston. This increased pressure forces open the ball valve 40 within the
compressor piston, allowing gas to move through the piston and into the
space below it which is part of the working space. As the compressor
piston begins to move back down the cylinder, the pressure above it
decreases, opening the compressor valve 50 and closing the ball valve 40.
This decreased pressure draws helium gas through the compressor tube from
the "buffer" space. This space is made up of the interior volumes of the
crankcase 10, the bell housing 88, and the generator housing 102. As the
compressor piston continues its up and down motion, it continues to
increase the pressure of the working space and decrease the pressure of
the buffer space. This increase in pressure of the working space causes an
increase in the rotational velocity of the engine.
Once the proper velocity is reached as determined by the micro-computer,
which is receiving input from the speed sensor 82, (previously used as the
starter commutator), a signal is sent to the pressure control valve 52.
This valve can be either a proportional valve or a pulse-width modulated
solenoid valve. As the pressure control valve is opened, working gas is
allowed to flow through the pressure control tube 54 which connects the
upper portion of the compression cylinder and the crankcase. This allows
the pressure of the working space to be decreased. A constant rotational
velocity can then be achieved by regulating the flow through the pressure
control valve, thus offsetting the increase in pressure caused by the
compressor piston. To achieve closed loop control of this speed regulation
a pressure sensor can be added to the system.
In order for a system with this simplicity to function properly, it is
imperative that no lubricating oil enter the working space. Such oil would
form a carbon build-up within the heater assembly and the regenerator. The
best way to ensure that no oil enters the working space is to eliminate it
entirely. To do this requires a careful selection of materials and
relationships of parts within the engine. For both the expansion and
compression pistons, a special flame sprayed coating consisting of ceramic
and PTFE is applied. This eliminates wear and provides a dry lubrication
between the pistons and the cylinder walls. A glass fiber reinforced and
PTFE impregnated material is used for the piston rings 62. High
temperature lubrication and seals are used in the self lubricated and
permanently sealed main bearings 78. The journal type connecting rod
bearings 72 are constructed of a graphite and PTFE filled sintered
polyimide. This material is self lubricating and can be operated at
temperatures of 500 degrees F., eliminating the need for lubrication or
crankshaft cooling.
To prevent overheating of the expansion piston and its piston rings, the
expansion cylinder is constructed in a way which allows the portion where
the piston and its rings travel to be water jacketed, and therefore
cooled, while the heater assembly, which forms the outer (away from the
crankshaft) portion of the cylinder and cylinder head, remains hot and is
thermally insulated from the expansion cylinder by a synthetic asbestos
material. Insulating the expansion piston from the hot working gas is the
fibrous ceramic dome which is solid but porous and has a rigid outer
ceramic layer. This material can stand extremely high temperatures, has a
very low coefficient of thermal conductivity, and has a density
sufficiently low as to allow its weight to be nearly equal to that of the
compressor parts that are attached to the compression piston, resulting in
a system that is balanced.
Conclusions, Ramifications, and Scope of the Invention
It can be seen that the Stirling engine generator system of this invention
provides a highly reliable, quiet, efficient and easy to manufacture,
therefore economical system. It is constructed with components which are
readily available in the industry such as automotive style crankshaft,
pistons, connecting rods and a conventional rotary generator. It has
overcome many of the problems associated with conventional internal
combustion engine driven generators, including vibration, noise,
pollution, and the consumption of expendable items such as lubricating oil
and filters, fan and alternator belts, alternator and starter brushes, and
mufflers. The present invention also overcomes many of the problems found
with previously disclosed Stirling engine systems, namely loss of working
fluid, complex control systems, dynamic balancing, and oil contamination
of heaters and regenerators.
While the above specification contains many specificities, these should be
regarded as illustrative rather than restrictive, and should not be
construed as limitations on the scope of the invention, but rather as an
exemplification of one preferred embodiment thereof. Variations and
changes may be made by those skilled in the art without departing from the
spirit of the invention. For example a double acting Stirling engine could
employ secondary pistons mounted inline with and connected to the present
pistons with rigid connecting rods which pass through an opening in an
intermediate bulkhead which separates the present cylinders with an
extension of same. This would achieve essentially a doubling of the power
output with little modification of the components. Similarly, four or more
cylinders could be employed either in line with the present cylinders or
radially around the crankcase, again doubling the power output.
It is well known that many heat sources can be used to power a Stirling
cycle engine, such as solar power. The replacement of the burner assembly
of the present invention with a solar collector or any other heat source
would not detract from the scope of the invention.
It is also well known that a Stirling cycle engine can be used as a heat
pump by simply running it "backwards". In other words supply input power
to an electric motor which replaces the generator of the present invention
and receive heat and cold as an output. It also should be noted that if
the generator of the present invention were replaced with another
identical Stirling engine, the result would be an efficient liquid fuel
(or solar) powered refrigeration system.
Other embodiments of the present invention could include a swash plate
drive, a rhombic drive or a system with cylinders essentially inline with
a crankshaft with a ninety degree angle between two lobes.
Accordingly, the scope of the invention should be determined not by the
embodiment illustrated, but by the appended claims and their legal
equivalents.
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